Video transmission and control system utilizing internal telephone lines

ABSTRACT

A video transmission system for facilitating transmission of video and control signals, particularly infrared remote control signals, between different locations in a residence using existing telephone wiring. Simultaneous transmission of signals of both types over active telephone lines is possible without interference with telephone communications. Transmission succeeds without requiring special treatement of the video signals beyond RF conversion, despite signal attenuation inherent in transmission over the telephone line media. Two or more video sources may be tied into the system, and selected as desired. Remote control signals generated in one room may be utilized without requiring a clear line of sight between the remote control device and the receiver.

BACKGROUND OF THE INVENTION

The present invention relates to a system for transmitting signalsbetween components of a video system over the telephone wiring of aresidence.

Until the late 1970's, it was very unusual for ordinary consumers to ownelectronic devices that generated or supplied video signals. Virtuallyall video programs viewed on television sets were received “over theair”. This situation changed over the past decade as VCRs, videocameras, cable converters, and home satellite systems became popular.

Currently, many consumers are able to watch video programs at differentlocations because they own more than one television set. When viewingprograms from one of the sources mentioned above rather than thosepicked up “over the air”, however, it is necessary to convey the signalfrom the video source to the television set. When source and receiverare located in the same room, connecting the two with a coaxial cable isusually the easiest method. VCRs and cable converters are nearly alwaysconnected to nearby television sets in this manner.

When the source and receiver are not located in the same area, a networkof coaxial cabling extending through the residence is a fine solution.Most residences, however, are not wired this way, or have networks thatdo not allow access at all desired locations. Furthermore, mostconsumers insist that the wiring be neatly installed or kept entirelyout of sight making installation of a network very difficult andunwieldy. This presents a problem when connection between a video sourceand a television requires wiring that extends between rooms, especiallyrooms located far from each other, or on different levels.

Today, it is very common for a residence to include a VCR and atelevision located in a “sitting room”, and a second television locatedin a bedroom. This has generated an enormous demand for technology thattransmits video across a residence without requiring installation of newwires. Possible solutions are to broadcast the signal at low power, orto use power lines or telephone wiring, which are always available, as aconductive path.

Broadcasting is currently not feasible in the U.S. because of FCCregulations, and is not feasible in most other countries for similarreasons. (Several consumer devices that broadcast video at low powerhave been marketed, however, despite their clear violation of FCCregulations. This testifies to the existence of a large demand fortransmission of video over short distances.) In addition to legalobstacles, the possibility of unintended reception of broadcast signalsoutside residences, and the possibility of interference from othersources broadcasting at the same frequency also present problems.

Regulations covering transmission between source and receiver overconductive paths are much less restrictive, and signals transmitted bythis method are much less likely to encounter interference from othersignals or be open to interception. Transmission across power wiring isvery difficult, however, because appliances typically attached to thosenetworks often impart electrical noise at many different radiofrequencies, creating a high potential for interference. Furthermore, areliable conductive path is not always available across “fuse boxes”,causing problems when source and receiver derive power from differentcircuits.

The difficulties in transmitting video by broadcasting or by conductionover power lines leave conduction over telephone wiring as the soleremaining option. This technique also involves very serioustechnological and legal challenges, however, and no solution has beenfound.

The most obvious difficulties are avoiding interference with telephonecommunications and conforming with all regulations that govern devicesthat connect to the public telephone network. Because telephone wiringin the US and many other countries typically includes four conductors,only two of which are used for communications in residences served by asingle telephone number, availability of the unused pair would seem topresent an interesting opportunity for avoiding these problems.Unfortunately, wiring installers often do not connect the unused pair atthe network junctions, leaving breaks in the conductive paths offered bythese wires.

The path supplied by the active pair, on the other hand, is guaranteedto be continuous between two jacks as long as telephone devices becomeactive when connected at those jacks. An exception is residences whereeach jack is wired directly to a central electronic switching unit thatprovides an interface to the public telephone system. The conductivepaths between jacks are likely to be broken across this unit.

There are other technical and legal problems associated withtransmission over this wiring beyond those created by the connection toa public or private telephone network. The technical problems derivefrom the fact that transmission of video was not a consideration whenstandards for wire properties, installation and connection techniques,and telephone electronics were established. Because these are allfactors that can influence the ability of the wiring to reliablytransmit high quality RF signals, this environment is poorly suited fortransmission of video.

Further legal problems derive from the fact that all RF signalsconducted across unshielded wiring will broadcast at least someelectromagnetic radiation. (Unlike coaxial cable, telephone wiring isnot shielded by a grounded metallic conductor that eliminatesradiation.) Because restrictions on RF radiation are very limiting inthe US and most other countries, they can potentially defeat anyparticular electronic technique that could otherwise successfullyachieve transmission.

Systems have been developed to transmit video signals over ordinarytelephone wiring, but none is practical for the residential applicationdescribed. Chou (U.S. Pat. No. 4,054,910) discloses a system fortransmitting video over an ordinary pair of wires without boosting thevideo signal in frequency. Video signals transmitted by devices thatfollow that design, however, would include energy at low frequenciesthat would interfere with telephone signals.

Tatsuzawa (U.S. Pat. No. 3,974,337) discloses a system that slightlyboosts video signals in frequency (by approximately 0.5 Mhz) to preventconflict with voiceband communications. The system also requires,however, a sophisticated procedure for compressing the bandwidth of thesignal so as to avoid use of energies at the higher frequencies, whichattenuate quickly. Further, the higher end of the resulting band is“preemphasized”, or amplified more than the lower frequencies, in orderto account for the remaining differences in attenuation.

The purpose of the technique disclosed by Tatsuzawa is to allow videosignals to travel distances on the order of 1 km or more. Theelectronics that reduce and expand the signal bandwidth however, arevery expensive. There is also a major difficulty in that the preemphasisof the signal must be adjusted depending on the distance between sourceand receiver. This is of significant inconvenience to a consumer.Further, the system depends on electrical characteristics particular tofrequencies between 0 and 4 Mhz, limiting the transmission frequency tothat band. This creates legal problems because in the U.S., for example,regulations severely limit the RF energy below 6 Mhz that can be fed towiring that is connected to the public telephone network. Finally, therestriction to a single band allows for transmission of only a singlesignal.

There are countless methods for reducing the resolution or the refreshrate of a video signal in order to reduce the bandwidth enough to avoidthe problem of attenuation, e.g. Lemelson (U.S. Pat. No. 4,485,400).Current video standards in the U.S. and elsewhere, however, use arefresh rate just quick enough to avoid annoying “flickering” of thepicture. Because most consumers have little tolerance for “flickering”or a reduced picture quality, these techniques do not present solutionsto the problem at hand.

Two commercially available devices are known by the inventors totransmit uncompromised video across telephone wiring. The first deviceis marketed by several cable equipment supply companies, e.g. the J411system marketed by Javelin Electronics of Torrance, Calif. The listprice of this device is nearly $1000.

The device transmits a single unmodulated video signal across thewiring. Because some of the energy of these signals is concentrated atfrequencies below 3 khz, the device will cause interference withtelephone communications. Further, the specifications stipulate that“transmission must be via dedicated twisted pair (of which telephonewiring is a subset) . . . and must be clean, unloaded, and unconnectedto any other device. The device also “pre-emphasizes” the signal byimparting more amplification at the higher frequencies, adding expenseand the inconvenience of requiring adjustment on the part of the user.

The second device, “Tele-Majic,” is marketed by Impact 2000, a catalogspecializing in consumer electronic devices. This device is composed ofa pair of identical connecting cables. These cables are advertised asenabling one to connect a video source to a residential telephone linein one area, and a television receiver in a second area, for the purposeof viewing the source at the second location.

Each cable consists of a classic matching transformer which connects tothe video devices, a capacitor for blocking telephone signals to preventinterference, and a telephone cord terminated with a “male” RJ-11 plug,the standard plug for connection to a telephone jack.

The device is intended to work by simply feeding the video signal fromthe source on to the wiring, and recovering it at a remote location. Forseveral reasons, it does not nearly solve the problem at hand.

To begin with, because “Tele-Majic” does not provide a video amplifier,the strength of the signal fed to the wiring will be limited by thestrength of the signal supplied by the source. This causes a problembecause the output signal levels generated by VCRs sold in the U.S. arelimited by law to approximately 10 dB re 1 mV into 75 ohms. At thislevel, the video signal can transmit only a few feet before the wiringwill attenuate its energy below the level required for qualitytelevision reception.

Beyond the limitations caused by low signal power, the matchingtransformer of the “Tele-Majic”, which constitutes half of theelectronics in the device, is significantly suboptimal, and does notteach anything about the correct purpose of that component.

In an apparent attempt to economize, the common 75 ohm/300 ohm matchingtransformer, built to connect between 75 ohm coaxial cabling and“twin-lead” wiring was chosen. Because matching transformers of the samedesign are included with virtually every video device sold in the U.S.,these are extremely inexpensive to obtain.

A matching transformer can serve the purpose of matching the impedanceof video equipment to telephone wiring. The impedance of typicaltelephone wiring, however is approximately 100 ohms at low VHF channels,not 300 ohms. This will create an impedance mismatch, and video signalswill lose more energy than is necessary when passing from the sourceonto the network via this cable.

The transformer can also serve the purpose of balancing the voltages onthe two leads of the telephone wiring, in order to reduceelectromagnetic radiation. Because the transformer used by “Tele-Majic”is designed to handle signals at all video frequencies, however, itcannot balance the video signal nearly as well as a transformerspecifically tailored for a specific frequency. The lack of balance willcause more radiation than would be released by a maximally balancedsignal.

Another problem is that complete isolation of telephone signals usingthe particular transformer supplied with the device requires twocapacitors rather than the single one which comes with “Tele-Majic”.This design flaw will cause total disruption of telephone communicationswhen the device is connected to a coaxial port whose outer shieldconnects to ground.

Given the ability to transmit video signals throughout a residence, theviewer of signals at a remote television remains limited in the abilityto control the apparatus that supplies the signal. Many video sources,especially VCRs and cable converters, are designed to cooperate withhand-held controllers that send out infrared control signals uponcommand of the user. Unfortunately, signals from these devices do nottravel between rooms unless there is a line-of-sight path betweentransmitter and source. It follows that a significant demand fortransmission of control signals should arise as a result of technologythat succeeds in transmitting video across telephone wiring.Furthermore, there is an obvious economy in achieving this transmissionusing the same wiring used for transmitting video.

Robbins (U.S. Pat. No. 4,509,211) discloses the only known method fortransmitting control signals from an infrared transmitter over atransmission line that also is used to transmit video signals. Thatmethod converts the infrared signals received in the area of atelevision to electrical impulses, which, due to the nature of typicalinfrared control signals, are concentrated at frequencies below 1 Mhz,lower than typical video frequencies. Those impulses are transmittedacross the transmission line to the area of a programmable video source,where they are converted back to infrared energy, recreating theoriginal light pattern.

The technology taught by Robbins, however, is not adequate forsituations where the energy of other signals sharing the transmissionline is concentrated at frequencies that fall within the frequency bandsthat confine the control signal energy. This is the case when activetelephone wiring serves as the transmission line. Under the methodRobbins discloses, signals from infrared controllers will conflict withtelephone communication signals because they both have informationcontent at frequencies between 0 and 3 khz. Any receiver that is tunedto frequencies between 0 and approximately 3 khz, such as a telephoneset, will react to both telephone signals and control signals. Eithertelephone communications will be noisy, or the infrared signals will beambiguous, or both. (If one signal is much stronger than the other, thatsignal may be received without distortion.) Furthermore, the system willfail whether or not video signals are present.

Robbins discloses devices that include, in combination with othertechnology, “isolation circuitry” which prevents the electrical signalsderived from infrared light patterns from reaching the video source andthe television receiver. Robbins teaches that “power lines, telephonelines or other existing conductor systems can be used, providing thevarious signals do not interfere, or providing isolation means areprovided.” This is incorrect. If two signals overlap in frequency, noisolation means will cleanly separate them so that only the desiredsignal reaches the receiver that is designed to react to it.

Indeed, the isolation circuitry disclosed is totally unnecessary evenfor the very application that is the focus of the Robbins patent. Underthe system Robbins discloses, video signals and control signals transmitacross a single conductive path at non-overlapping frequencies, andisolation circuitry is provided to block the control signals from thevideo source and the television receiver connected to this path. BecauseVCRs and virtually all other video sources have reverse isolationprovided at their output ports, electrical energy incident at theseports will have no effect at all, and extra isolation is not required.Further, when a television is tuned to a particular video channel,signals at frequencies outside of that channel are ignored unless theirenergy level is very high. The control signals will be ignored in thismanner, just as video signals at VHF channel 3 and VHF channel 5 areignored by a television receiver tuned to VHF channel 4.

Beyond Robbins incorrect teaching of isolation circuitry and the factthat the infrared transmission system he teaches is inadequate for thepresent application, Robbins teaches nothing regarding transmission ofvideo over telephone wiring.

An electronic transmitter/receiver pair called the Rabbit follows theelectronic principles disclosed in Robbins patent to send video andinfrared signals between a VCR and television. This device, which citesthe Robbins patent on its packaging, has been available at retailoutlets since 1985. It uses a transmission line composed of a singlevery thin insulated wire pair which must be installed by the userbetween the VCR and a television. Thus, it embodies the very difficultythat the current invention seeks to address.

There is another system known for transmitting infrared signals from atelevision to a remotely located VCR, but it differs in that it usesbroadcast technology rather than a transmission line. Called the “RemoteExtender” and marketed by Windsurfer Manufacturing of DeFuniak Springs,Fla., this device converts the infrared signals to electrical impulses,then boosts these impulses to a UHF frequency and feeds them to anantenna from which they broadcast. A remotely located receiver picks upthese UHF signals, downshifts them back to their original frequencyband, and uses the resulting impulses to recreate the original infraredpattern.

Because this system uses broadcast technology, it is much moresusceptible to interference, and its receiver has the potential ofmistakenly picking up control signals from the transmitter of a secondtransmit/receive pair operating nearby. Furthermore, it is obviouslymore economical to use the telephone wiring for transmitting controlsignals when combining with technology that transmits video using thatmedium.

The simultaneous transmission of infrared control signals and a singlevideo signal across telephone wiring is the major focus of thetechnology disclosed herein. It is easy to see, however, the usefulnessof extending this technology to allow signals from more than one videosource to transmit at a given time.

When each source transmits a signal at a different frequency band, thetelephone wire medium should present no barrier to the use by multiplesources. Many factors, however, limit the number of bands that areavailable. An especially restrictive limit, of course, is imposed by thedifficulties of using telephone wiring as a medium. In the event thatthe number of desired sources exceeds the number of available channels,this limit becomes restrictive.

If a viewer can disable all but one of multiple sources that use thesame band, however, the picture from the remaining source can bedisplayed without interference. This possibility creates a demand for atechnique that allows a user to quickly, conveniently, and remotelyactivate one of several sources that are connected and ready totransmit.

SUMMARY OF THE INVENTION

In view of the foregoing, one object of the present invention is toovercome the difficulties of transmission of video signals and controlsignals from infrared transmitters across active networks of telephonewiring.

In accordance with this and other objects, the present inventionincludes a pair of transceivers: a first transceiver which is designedfor connection between a video source and a telephone jack or other portof access to a network of telephone wiring, and a cooperatingtransceiver which is designed for connection between an ordinarytelevision receiver and a telephone jack. These transceivers takeadvantage of the simple two-wire conductive paths provided by the wiringof ordinary residential telephone systems, and thus provide thefollowing results, in stark contrast to known techniques discussedabove:

1) Each television that is connected via a transceiver can display, inaddition to any of the other signals otherwise available to it, thesignal from any video source connected via a cooperating transceiver asdescribed above.

2) An unlimited number of televisions can connect and operatesimultaneously. Each television can select any of the connected sourcesfor display at any time, as long as the source is active, i.e.conducting its signals onto the telephone network wiring.

3) The number of sources that can be active at once will depend on manydifferent factors, but will always be greater than one. The signals fromeach active source occupy different, non-overlapping frequency bandswhile transmitting across the wiring.

4) Any number of sources can share a single frequency band, but only oneof that group can be active at a given time. The transceivers thatconnect to the video sources will include one of two technologies forallowing a viewer at any television to remotely and conveniently switchthe identity of the active source that is using a particular band.

5) Any video sources that respond to control signals from infraredtransmitters and are connected via a transceiver as described above canbe controlled from any area where a connected television is located,whether or not such area is within a line of sight of the video source.

6) Operation of telephone and other low-frequency communication,including that conducted by intercoms, fax machines, and modems, is notaffected by the connection and operation of any of the devices hereindescribed.

7) All of the capabilities described above are provided by simpleconnection of the transceivers. No other effort on the part of the useris required.

In addition to these and other objects and results, a design isdisclosed for a special television that connects directly to a telephonenetwork. This television is designed to cooperate with the video sourcetransceiver mentioned above. It includes electronics for deriving videosignals from the wiring and tuning to them, and will transmit theintelligence of infrared control signals that it detects back over thewiring to the transceiver for control of its connected video source.Like the transceivers, it causes no interference with telephonecommunications.

A further design is disclosed for an inexpensive device that, incombination with the disclosed transceivers and television, provides theabove capabilities to residences equipped with special telephone systemsthat include a central electronic switching unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram that illustrates the fundamental components ofthe video source transceiver and how those components interact with oneanother.

FIG. 2 is a block diagram that illustrates the fundamental components ofthe transceiver that connects to a television and how those componentsinteract with one another.

FIG. 3 is a chart which describes the three systems disclosed forcooperation between RF conversion components of the two transceivers.

FIG. 4 is a block diagram showing how special components can be includedwithin an ordinary television to provide for recovery of video signalsfrom active telephone networks and for transmission of control signalsonto those networks for reception by a cooperating transceiver.

FIG. 5 shows the electronics of an adaptor designed to allowtransmission of RF energy across telephone networks that include acentral switching unit.

FIG. 6 shows the electronics used within the video source transceiverfor coupling to an active telephone network.

FIG. 7 shows the electronics used within the transceiver that connectsto a television for coupling to an active telephone network.

FIG. 8 shows the details of the circuitry that converts infrared lightto electrical energy at frequencies above the telephone voiceband.

FIG. 9 shows the details of the circuitry that creates an infrared lightpattern from an electrical signal above the telephone voiceband.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The devices disclosed herein provide for transmission of video signalsand control signals from infrared transmitters across active networks oftelephone wiring without affecting ordinary telephone communications.They are designed to accommodate video signals with the same resolutionsand refresh rates as those used for public broadcasting. Whentransmitting signals across path lengths typical of those found inordinary residences, the devices provide enough signal fidelity toproduce undegraded images and unambiguous control commands.

Design of these devices required an extensive experimental andtheoretical investigation of the physics of transmission of videosignals across this type of network, a deep appreciation of the specialneed for convenience and economy in consumer products, some circuitdesign, as well as a novel combination of electrical signal processingcomponents.

A description of the disclosed devices is preceded by an overview of thetopic of transmission across telephone wiring. The overview will beginwith a summary of the investigation into the transmission of video andwill conclude with a description of the method designed to transmitsignals from infrared controllers.

The descriptions that follow the overview include several options forthe design of the pair of cooperating transceivers, the specialtelevision/transceiver pair, and the special adaptor referenced in thesummary. The influence of the transmission investigation on thesedesigns as well as the influence of other considerations related toconsumer electronics will be included in those descriptions. Theadvantages and disadvantages of the various designs will also bediscussed, and the preferred embodiment will be identified. Finally, theelectronic details of some circuitry described in general terms earlieron will be presented.

The signals described as video herein refer to signals that providepicture information encoded according to NTSC, PAL, SECAM, or similarformats that are used for public broadcasting throughout the world.These formats provide between 50 and 60 image frames per second, andvertical resolutions of between 525 and 625 lines per frame.

In general, the disclosed devices are designed to transmit audioinformation along with video according to these formats. Most of thedisclosed technology, however, will function the same whether audio ispresent or not. For this reason, signals described as video shall referto signals with or without audio information. An explicit descriptionwill be used whenever audio is specifically included or excluded.

Transmission of Video Signals Across Telephone Wiring

The following problems must be overcome for transmission of videosignals to succeed across a network of telephone wiring:

1) Multi-path effects, also known as “reflections” or “ghosting,” cancause video distortion. These effects can arise in a network of wiringbecause signals can travel from source to receiver via many differentpaths. If signal energy arrives at the receiver across two paths thatdiffer in length, the signal conducted across one path will be offset intime relative to the signal traversing the second path. This will causethe same image to appear at two different points in the scanning cycleof the picture tube. This can create the special distortion patterncalled “ghosting” if the offset difference is large enough. Multipath“ghosting” of broadcast signals is commonly caused by large buildingsthat reflect broadcast energy and create multiple paths of significantlydifferent lengths to nearby antennae.

2) Reduction of signal energy across the transmission paths can reducethe signal-to-noise ratio present at a television receiver below thatrequired to produce a high-quality picture. A signal-to-noise ratio of40 dB is marginally sufficient for high-quality video. It follows thatpicture degradation will result whenever signal energy at the receiverfalls to within 40 dB of the noise level on the wiring or the minimumnoise floor of the television receiver.

Three factors are principally responsible for attenuation of the energyof the signal as it travels from source to receiver, resulting in alower energy at the end of any transmission path. These factors are:

a) Attenuation or dissipation of signal energy by the wiring. Unlikecoaxial cable, over which video signals travel with little attenuation,telephone wiring dramatically attenuates high frequency energy. Thisattenuation increases linearly with path length, and also increases withfrequency. At 90 Mhz for example, typical telephone wiring attenuatesenergy at 14 dB per 100 feet, while at 175 Mhz, attenuation isapproximately 25 dB per 100 feet.

b) Network junctions where the wiring splits. These can causesignificant attenuation when they occur on one of the principal pathscarrying energy from source to receiver. When the alternative path isvery long, the energy splits, reducing the level on the maintransmission path by approximately 3.5 dB. As the alternate path becomesshorter, attenuation will depend on whether or not the branch is open,or “terminated.” If the branch is unterminated, attenuation will be lessthan this amount, and will be negligible for very short branches. Athigher frequencies, the 3.5 dB limit is approached more quickly.

c) Telephone devices that dissipate high frequency energy. A significantnumber of these devices exhibit this property. If they terminate shortbranches, as described above, they can drain energy from a principaltransmission path. Devices that have a strong dissipative effect canreduce the energy beyond the ordinary 3.5 dB splitting loss. As thelength of these branches increases, the attenuation of the branchprevents the draining phenomenon, and the ordinary 3.5 dB splitting lossbecomes the dominating factor. At higher frequencies, the 3.5 dB limitis encountered at shorter path lengths.

3) The fact that attenuation increases with frequency can cause theenergy near the high end of a 6 Mhz video channel to attenuate more thanthe energy at the lower end. This causes a “tilt” in the signal powerspectrum, which is a form of signal distortion that can cause picturedegradation if it is sufficiently pronounced.

4) Interference from strong broadcast signals picked up by the wiringacting as an antenna can cause severe distortion. The ability of thewiring to receive broadcast energy increases with frequency.

5) Because telephone wiring, unlike coaxial cable, is not shielded by agrounded metallic conductor, significant electromagnetic radiation canbe created when it conducts electrical energy at radio frequencies. Thiscan create legal problems as well as interference to nearby televisionsand other receivers tuned to those frequencies. The level of radiationcaused by a given signal level increases with frequency. (In contrast toreguations covering radiation, no special legal problems are created inthe U.S. by the connection of radio frequency devices to the publictelephone network if those devices do not transmit energy below 6 Mhz.Restrictions are not required because the network wiring will quicklyattenuate such energy below any meaningful level.)

One possible strategy for addressing these problems is to recode thevideo signal into a different waveform with equivalent informationbefore imparting its energy to the wiring. If, for example, thebandwidth of the signal could be compressed without losing information,the problems of tilt, interference, and, possibly, radiation would bereduced. Implementation of compression or other recoding techniques,however, is extremely expensive, and will probably not significantlyalleviate all of these problems.

Because some conventions for video encoding and modulation providesignals with redundant information, the bandwidth of a video signal cansometimes be reduced by sharp filtering without significant loss-ofinformation. Because the potential reduction would not be large,however, this strategy is also unlikely to significantly alleviate theproblems described above.

A second method of waveform alteration is to amplify the higherfrequencies of the signal more than those at the low end. This is called“pre-emphasis” and can compensate for “tilting” of the signal. Apartfrom the fact that it only addresses one of the potential problems,however, pre-emphasis is expensive, and also requires the inconvenienceof adjusting the compensation level upon installation in a newresidence. This is because the attenuation differential is a proportionof the overall attenuation which, in turn, will vary from one residenceto another.

Beyond rewiring a residence, which defeats the purpose of the invention,the only other elements of control that can be exercised to helptransmission succeed lie in the choice of the energy level andfrequency, and in electronics that can limit the effects of theconnected telephone devices. Most individuals skilled in the art,however, expect that an amplified video signal conducted acrosstelephone networks would suffer from “ghosting” at most any frequencyand energy level. Others suspect that amplification of the signal highenough to force it across the wiring would create completelyunacceptable levels of radiation.

To investigate transmission over this network, the inventors devised andconducted a series of experiments that included observation of thequality of pictures generated from transmitted signals, and alsomeasurements of radiation created by the transmitting signals.

As part of the experiment, a transmit/receive pair was designed, usingtechnology disclosed later herein, to feed amplified video signalsthrough one port on a network and to recover them from a second port.These devices were used to perform experiments in twenty residencesusing video signals at different energy levels and frequencies. For mostof the experiments, telephone equipment was disconnected at the involvedports, but some remained elsewhere on the network. A few tests wereperformed to investigate the effects of telephone equipment sharing thesame port.

The radiation tests involved conduction of video signals on to anunterminated 50 foot length of wiring that was extended horizontally andelevated one foot above ground, and measuring field strength via acalibrated antenna placed 3 meters from the midpoint of the wire. Thesignals were conditioned to minimize radiation before they were fed towiring. The conditioning involved a process called “balancing”, which isused in the disclosed transceivers and is described later on.

The most natural choices for transmission frequencies are the channelsin the low VHF range. In the U.S., the low VHF range is composed of VHFchannels 2 through 6, which extend from 54 Mhz to 88 Mhz. VHF channels 2through 4 constitute one adjacent group of three 6 Mhz wide channelsspanning between 54 Mhz and 72 Mhz, and VHF channels 5 and 6 constitutea second adjacent group spanning from 76 Mhz to 88 Mhz.

Channels in the low VHF range are good candidates for transmissionfrequencies because they constitute the lowest group of channels tunableby ordinary televisions. The benefit of tunability is that televisionreceivers can recover these signals from the wiring in tunable form,eliminating the need for electronics that convert their frequency. Thebenefits of using the lower frequencies among the VHF channels are theattendant reductions in attenuation and radiation.

A further advantage of tunability is that if the channel is not used forlocal video broadcasting, there is no possibility of is interferencefrom broadcast energy picked up by the wiring in the U.S. That isbecause the frequency bands allocated to video broadcasting in the U.S.are off limits to any other services.

Because little variation was expected across the low VHF range, testswere conducted only at VHF channel 3. No frequencies above this rangewere tested because the first tunable channel above VHF channel 6 is VHF7 which, at 174 Mhz, would exhibit significantly greater attenuation andradiation, and would have no redeeming advantages over the low VHFchannels.

To see if further reductions in attenuation and radiation would offsetthe extra costs associated with using channels below the tunable range,it was decided to investigate transmission at frequencies below VHFchannel 2. Because U.S. Federal Communications Commission radiationlimits are less restrictive below 30 Mhz, it was decided to choose thechannel spanning from 24 Mhz to 30 Mhz.

To the inventors' knowledge, the only applications involvingtransmission of video signals with high resolutions and refresh rates atfrequencies below the tunable range are those where extra bandwidth isneeded on a cable TV distribution network. This requirement can arisewhen there is a need to send video signals over cable from remotelocations back to a central transmission site. These frequencies areavailable for reverse transmission because distribution systems do notordinarily use frequencies below VHF channel 2. They are not tunable bytelevisions and have never, to the inventors' knowledge, been used inany consumer video device.

Following is a summary of the results of the transmission and radiationexperiments:

1) When a VHF channel 3 signal with a conducted energy level of 37.5 dBre 1 mV was fed onto the wiring at the source end, visibly undegradedpictures were generated from signals recovered at a remote jack in 85%of the test cases. Radiation from signals at this energy level weremeasured at approximately 200 uV/M at 3 meters.

2) At an energy level of 42.5 dB re 1 mV, video signals concentratedbetween 24 Mhz and 30 Mhz succeeded in generating a visibly undegradedpicture in 100% of the test cases. Radiation levels were approximately200 uV/M at 3 meters. (This level was the same as the level for VHFchannel 3 because a higher conducted signal level was used.)

3) Ghosting was never observed at any frequency or energy level.

4) Interference from a broadcast video source distorted the picture onlywhen it was strong enough to create an undegraded picture via antennareception. Distant video sources caused no interference. This type ofinterference, of course, applied only to the tests at VHF channel 3 andnot at the 24 Mhz to 30 Mhz channel.

5) Signals from CB radio transceivers, which operate with 5 watts ofpower and span the range from 26.965 Mhz to 27.4 Mhz caused interferencewith transmission across the 24-30 Mhz video channel when a CBtransmitter was within 50 feet of the telephone wiring. Interferencefrom other sources was not noticed, but is obviously possible when asource transmitting at an interfering frequency is close enough ortransmits with enough power.

6) The connection of telephone equipment at ports previously used onlyby the transceivers occasionally degraded an otherwise high qualitypicture.

7) No distortion that was noticed could be traced to “tilting” of thesignal spectrum.

8) Radiation from signals transmitting across the wiring at VHF channel3 often caused slight but significant interference to nearby televisionstuned to a VHF 3 signal supplied by a different video source. Thisoccurred most often when a cable converter and VCR both connected to atelevision receiver, and the television tuned in a signal from the cableconverter at VHF channel 3 while the VCR supplied the VHF 3 signal thatwas transmitted across the telephone wiring. This type of interferenceoccurred on older televisions that did not offer a shielded input port,and also on more modern televisions that connected via a shieldedcoaxial cable but allowed slight leakage from other available ports suchas twin lead ports. Note that this type of problem will not arise whenusing VHF channels 5 or 6 for transmission across the wiring, becausevideo sources that supply signals at those channels are very rare.

The survival of enough signal energy to generate a quality picture canbe explained by simply considering the attenuation expected over thelongest paths typically encountered in residences. If one assumes aminimum television receiver noise figure of 5 dB, a receiver bandwidthof 6 Mhz, and a desired signal-to-noise ratio of 50 dB, one finds thatthe minimum signal level required at the receiver is 770 uV into 75ohms. The output level of a typical VCR is approximately 2000 uV intothe same impedance, well above the minimum necessary to reliably providea high quality picture. At 66 Mhz, attenuation of signals transmittedover telephone wiring is approximately 30 dB over 250 feet. It followsthat 30 dB of amplification should ensure good signal quality over thelongest paths in typical households, except where splits in the wiringand connected telephone equipment cause excessive attenuation.

The lack of “ghosting” can be explained by the fact that there isusually a monotonic relationship between signal transit time andattenuation. (The rare exceptions to this relationship can be caused bya short path over which signals suffer extraordinary attenuation due tothe presence of many splits, or the presence of telephone devicesconnected off short branches. Signals traversing such a path mightattenuate more than those traversing a longer path that has a longertransit time.) Because of this monotonic relationship, secondary signalsarriving at the receiver after traversing long reflected paths will beusually be significantly attenuated relative to signals that travel overthe most direct path from the transmitter. The “offset” in the picturethat produces “ghosting” is related to the difference in travel times.To be visible, the offset must be at least as wide as the resolution ofthe television. It can be shown that path length differences that createoffsets this large also have enough difference in attenuation to placethe energy level of the reflected path at least 40dB below that of theincident path, which is below the minimum SNR required for a qualitypicture, making the reflected energy negligible and its interferenceinvisible.

The results of the experiments verified that when two signals are fed totelephone wiring at energy levels that will cause them to generate thesame amount of electromagnetic radiation, a signal transmitting at achannel below 54 Mhz has a significantly higher probability ofgenerating a high quality picture than a signal transmitting at a lowVHF channel. Transmission at lower frequencies, however, is moresusceptible to interference from broadcast sources and also requiressomewhat more expensive electronics.

Transmission of Signals from Infrared Controllers Across TelephoneWiring

As described in the introduction, the second signal that will be passedbetween the transceivers is the control signal from an infraredtransmitter operating in the area of a connected television. Part of thedisclosed transmission technique follows the known strategy oftransducing the light pattern created by these signals into electricalenergy and transmitting that energy across the wiring in the oppositedirection of the video signals, to be received by the transceiverconnected to the video source. That transceiver uses the electricalversion of the signal to recreate the original infrared light pattern,for the purposes of controlling the video source to which it connects.

The technique disclosed herein embodies an extension designed to avoidinterference with telephone signals. The extension calls for thefrequency of the electrical version of the control signals to beconverted to a higher band before transmission across the wiring. Thisband will be high enough to eliminate interference with telephone orlow-frequency communication signals. After recovery of this signal atthe end of the transmission path, the signal is converted back to itsoriginal band before being used to recreate the original light pattern.

Maintaining the fidelity of the control signals across the wiringpresents less of a challenge than was posed by transmission of videosignals. Unevenness, or “tilting” in the signal spectrum is not aproblem because the bandwidth of the signal is small. An analysis of thefactors governing multi-path interference indicates that that problemshould not arise either.

Because the bandwidth of control signals from typical infraredtransmitters is considerably less than 1 Mhz, finding a frequencyinterval that will encounter little interference from ambient broadcastsignals is not difficult. Also, the information content is small so thatlittle energy is required for successful transmission. The reducedenergy generates less radiation.

Other requirements for the choice of a frequency band and energy levelfor transmission of these signals are that the band must not overlap, ofcourse, the video signals at the frequencies chosen for videotransmission, and the energy must meet the legal requirements thatgovern devices that connect to the public telephone network. Asmentioned earlier, the U.S. Federal Communications Commission imposes norestrictions on signals above 6 Mhz, leaving ample room between thatfrequency and the video signals, even if a channel below VHF 2 is used.The control signals can also be transmitted above the frequencies usedfor transmission of video.

A frequency centered at 10.7 Mhz is used in the preferred embodimentbecause that is a common intermediate frequency in FM radio devices, theresult of which is that there are very inexpensive electronic componentsavailable that are especially suited for that frequency.

Description of the Transceiver that Connects to a Video Source

As a result of the investigation into transmission of video signalsacross active telephone wiring and the system adopted for transmissionof control signals, a general design for a transceiver was developed toconnect between a video source and telephone wiring to perform thefunctions of:

-   -   1) shifting the frequency of the video signal from the channel        supplied by the source to the channel used for transmission,    -   2) amplifying the video signal,    -   3) “balancing” the two leads of the video signal so that their        voltages are nearly equal and opposite with respect to ground,        and matching the impedance of the telephone wiring,    -   4) transmitting this signal on to the telephone network without        disturbing low-frequency communication signals, simultaneously        recovering the control signals fed to the wiring by the        transceiver connected to the television,    -   5) downshifting the control signals to their original frequency,    -   6) using the resulting energy to recreate the original infrared        pattern, and    -   7) connecting to a telephone jack while allowing for telephone        devices to share the same jack without loading down the energy        of the video signal.

FIG. 1 shows an arrangement of electronics for a transceiver 1 designedto implement these functions. This transceiver is described in thefollowing paragraphs. The description discloses several optional designvariations.

The transceiver 1 connects to the video source 2 to derive a signal.That signal is passed to RF converter 3, which translates the signal tothe frequency band chosen for transmission over the wiring.

Fortunately, nearly all consumer video sources provide their signals inone of only two different ways. Some devices provide an unmodulatedvideo signal containing no sound information from one port and anunmodulated audio signal from a second, separate port. Others supply avideo signal, possibly including sound information, at either VHFchannel 3 or 4, according to a switch set by the consumer. Most VCRsmake their signal available in both forms.

Two alternative design options for RF converters are disclosed fortransmission at a low VHF channel. These options have clear advantagesover all other possible designs. One design derives the signals from theport that supplies a low VHF signal, hereinafter referred to as the “lowVHF port.” That design is described first. That description is followedby a description of the second design, which derives its signal from theport that supplies an unmodulated signal, hereinafter referred to as the“baseband” port.

Operating manuals for video sources that provide a VHF channel 3 or 4signal instruct users to select the channel not used for localbroadcasting. One of the two is always guaranteed to be free frombroadcast interference in the U.S. This is because the U.S. FCC hasallocated frequencies to ensure that no locality has broadcasting atboth of two adjacent video channels, and has reserved the videobroadcast bands strictly for television.

It follows that the low VHF port on a VCR is guaranteed to provide a lowVHF signal that is not used for local broadcasting. This eliminates theneed for RF conversion electronics and significantly reduces the expenseof the device. Furthermore, a single design can suffice for everylocation in the country.

A possible drawback to this alternative is that of the interferenceproblem, described earlier, caused by radiation of the transmittedsignal from the wiring that leaks into televisions deriving signals froma separate source at VHF channel 3 or 4. To minimize radiation and thusalleviate this problem, the use of a special connecting cable and avariable amplifier are disclosed later on in the description of thistransceiver.

The second design option for transmission at a low VHF channel calls forthe signal to be derived in unmodulated form from the baseband port.This option has two significant advantages. One is that the low VHF porton VCRs is usually connected to a television receiver, while thebaseband port on VCRs is almost always unused and open, makingconnection of the transceiver extremely easy.

The other advantage derives from a switch, usually referred to as the“TV/VCR” switch, that controls the output of the low VHF port on VCRs.The TV/VCR switch allows the VCR signal, created from a video tape orfrom a signal tuned in by the VCR tuner, to be sent out at VHF channel 3or 4, or alternatively, it allows the signals input to the VCR-to passout the “low VHF” port at their original frequencies. Meanwhile, the VCRsignal always exits the baseband port. This allows the local televisionto tune to either the input signals, or to the signal produced by theVCR, while the VCR signal exits the baseband port separately, availablefor transmission-across the wiring to the remote television. Moreover,the “TV/VCR” switch usually responds to one of the controls on anaccompanying infrared remote control transmitter.

If a low VHF frequency is chosen for transmission and the baseband portis chosen as the signal source, the RF converter 3 is obviouslyrequired. The converter inputs a video signal, and uses that signal tomodulate a low VHF carrier signal, creating an equivalent video signalat a low VHF frequency. (If an audio signal is available, it wouldordinarily make sense, of course, for the modulator to combine thissignal together with the video according to the NTSC or an equivalentformat, and then use the combined signal to modulate the carrier.) Inorder to achieve the economy provided by a single design that sufficesfor the entire U.S., one of two adjacent low VHF channels should be madeavailable and set according to a user-controlled switch. (Theoretically,the switch could also be automatically controlled, using circuitry thatdetects the presence of broadcast energy to choose the empty channel.) Adesign for this modulator is not given because several designs are wellknown.

Several advantages accrue if the modulator is designed to operate ateither VHF channel 5 or 6, instead of the other two available adjacentlow VHF pairs: VHF 3/4, and VHF 2/3. First of all, the special problemof radiative energy from the wiring interfering with the signal providedby a separate video source to a nearby television will not occur. Thisis because consumer video sources seldom provide their video signal atVHF channel 5 or 6. Secondly, the television connected via thetransceiver will more easily be able to combine the recovered signaltogether with a local video source, such as a cable converter, againbecause video sources almost always use VHF channels 2, 3, or 4.Finally, an advantage accrues from the fact that VHF channels 5 and 6are not adjacent to any other channels. This means that when combiningthe telephone line signal with a signal from an antenna, the signal fromthe telephone line will never be adjacent to more than one broadcastsignal. Because only expensive modulators confine their signalscompletely within their intended band, this reduces possibilities ofinterference.

The RF converter 3 is also required, of course, if a frequency below VHFchannel 2 is used for transmission, independent of the port from whichthe video signal is derived. Unlike low VHF channels, however, channelsbelow VHF 2 are not tunable by ordinary televisions, making REconversion a requirement at the transceiver that connects to thetelevision, shown later in FIG. 2. The RF conversions performed by thetwo transceivers must obviously coordinate in this case. Three systemsfor coordination between these conversion operations are disclosedfollowing the description of the television transceiver.

After it is derived at or shifted to the channel used for transmission,the video signal is passed to an RF amplifier 4, which increases theenergy level by a fixed factor. In order to increase the likelihood ofsuccess of transmission across all residences, amplification should beset to cause radiation that barely meets legal limits, unless a veryhigh success rate can be achieved with a lesser setting.

A variation of this design calls for an RF amplifier 4 that allows theuser variable control over the amplification level. This is valuable insituations where VHF 3 or 4 is used for transmission, because radiationfrom the wiring can cause interference at televisions connected toseparate sources, as described earlier. A variable reduction of signallevel potentially enables a user to eliminate this interference whilekeeping signal level at the remote television high enough to generate anundegraded picture.

After amplification, the video signal follows the conductive path to acoupling network 5. This network 5 feeds the video signal to thetelephone wiring, and allows the control signals from the televisiontransceiver to pass from the wiring towards the control signalprocessing circuitry 6. (The process whereby control signals from aninfrared transmitter are converted to electrical energy above voicebandand conducted on to the telephone line is included within thedescription of the television transceiver.) The network also performsthe functions of balancing the energy of the video signal, matching theimpedance of the video signal path to the impedance of the telephonewiring, blocking low-frequency telephone communication signals from thetransceiver electronics, and blocking the flow of video signals towardsthe control signal processing circuitry 6. The network 5 does not blockthe flow of control signals towards the RF amplifier 4.

The importance of these functions is described in the followingparagraphs. The detailed electronic design of the preferred embodimentof this network is shown in FIG. 6 and is described in detail later on.

Balancing the video signal energy on the two leads of the wiringpromotes cancellation of the two electromagnetic fields created by theseleads, dramatically reducing radiation. The frequency of the input willhave the biggest effect on the balance achieved by a given networkdesign. Because the frequency will be known, the design can be tailoredto produce a reliable balancing.

Balancing of the control signals, on the other hand, is not nearly ascritical because the strength of those signals can be boosted highenough to guarantee quality transmission while limiting radiation tolevels below legal or otherwise significant limits.

The impedance of the internal transceiver circuitry wiring is matched tothe impedance of the telephone line at the video frequencies becausetransition from one medium to another is inefficient and wastes signalenergy if impedance is not matched. This can be important in situationswhere the video signal energy is only marginally high enough to create ahigh quality picture. Impedance matching at the-frequencies used bycontrol signals is not important because of the excess power availablefor transmission of those signals.

Blocking low-frequency signals from transmission to the electronics ofthe transceiver prevents any interference with ordinary telephonecommunication signals. The blocking should render the connection andoperation of the transceiver totally transparent to the functioning oflow frequency telephone communications.

Blocking the flow of video energy to the control signal processingcircuitry 6 allows that component to reliably recreate the originalcontrol signal without special expensive electronics. The video signalwould ordinarily disrupt this processing because it has a very highenergy level while passing through this network.

Note that the network 5 allows control signals to pass on to the RFamplifier 4. There is no need to block these signals because they willbe at frequencies above baseband and RF amplifiers are commonly designedto terminate low power RF signals that are incident at their outputs.The amplifier thus provides isolation of the control signal from thevideo source as a side effect. If this intelligence could traverse theamplifier and transmit to the RF converter 3 or the video source 2, itwould be similarly ignored, because these devices also commonly providereverse isolation.

The function of the control signal processing circuitry 6 is todownshift the frequency of the control signals back to their originallocation at baseband, and to use the resulting energy to drive aninfrared emitting bulb 7, recreating the original light pattern. Thisfunction completes the process of transmission of signals from aninfrared transmitter over active telephone wiring, s a function notheretofore a part of any commercial or consumer device. The preferredembodiment of the control signal circuitry 6 of the video sourcetransceiver is shown in FIG. 9 and is described in detail later on.

If the video source transceiver is placed on top of the source to whichit connects, which seems likely to be the most convenient placement,there will not be a line of sight path between the infrared bulb and theinfrared sensitive pick up window on the source. This is not a problemif the infrared light can reflect off walls and retain itseffectiveness, something that is known to be possible. To allow thisconvenient placement of the transmitter, the infrared transmission bulbshould be driven at high power and with a wide beamwidth, in order todecrease the possibility of insufficient reflective energy. It may makesense to drive several bulbs oriented at different angles.

The transceiver 1 connects to the telephone network 10 via a connectingcord 12 terminated with a male RJ-11 plug, the standard plug used toconnect to telephone jacks. This cord includes two special components: atouch tone switch 8, and a low pass filter 9. Also, the two conductorsof the cord are systematically twisted about each other.

The touch tone switch 8 is an optional feature provided for coordinationof this transceiver with other video source transceivers connected tothe same network. Its function is described in detail later on. For thepurposes of the current discussion, it can be assumed that the switchhas no influence on signal flow across the cord 12 or on the operationof the other components. The other two features, the low pass filter 9and the special nature of the conductors of the cord, are described inthe following paragraphs.

As mentioned earlier, telephone devices that connect to a maintransmission path via a short stretch of wiring can cause significantdissipation of RF signal energy. To allow equipment to remain connectedat the ports shared by the transceiver without causing attenuation, thelow-pass filter 9, consisting of two induction coils with low-passproperties; connects in series to the two conductors of the cord tooffer a second port for connection of telephone equipment 11. Thisfilter removes most high-frequency effects of both the equipment and thesplit in the wiring by presenting a high impedance to RF signals.

Twisting the conductors of the cord significantly reduces the energythat radiates from those conductors, beyond the reduction that derivesfrom balancing the voltages. When used in combination with the low-passfilter, this feature leaves only the wiring connecting the jacks to thepublic telephone interface, and the wiring connecting telephone devicesat uninvolved jacks as a source for significant radiation. (If theconnecting wires are twisted, and uninvolved jacks are far from the maintransmission path, very few radiation opportunities will remain.) Thisreduction is important for the case where a television receiving asignal from a separate video source encounters interference fromradiation generated by the wiring at VHF channel 3 or 4.

Shielding of the conductors by a metallic conductor also will reduceradiation. This shielding is more effective if the conductor isconnected to ground.

Description of the Transceiver that Connects to a Television Receiver

Based on the system adopted for transmitting infrared signals, and therequirements for conveniently supplying video signals to a televisionreceiver, a general design for a transceiver was developed to connectbetween telephone wiring and a television receiver to perform thefunctions of:

-   -   1) receiving ambient infrared control signals, converting them        to electrical energy, and boosting the frequency of this energy        to a band that lies completely above the frequencies used for        ordinary telephone communications,    -   2) feeding the control signal on to the telephone network        without disturbing low-frequency communication signals, while        simultaneously recovering video signals,    -   3) matching the impedance between the telephone wiring and the        conductive path that receives the video signal,    -   4) converting, if necessary, the received video signal up to a        channel that is tunable By a television and is not used for        local broadcasting, and    -   5) connecting to a telephone jack while allowing for telephone        devices to share the same jack without loading down the energy        of video signals on the wiring.

FIG. 2 shows an arrangement of electronics for a transceiver 15 designedto implement these functions. This transceiver 15 is described in thefollowing paragraphs. The description discloses several optional designvariations.

An infrared sensitive diode 16 reacts to control signals from aninfrared control signal transmitter 23 to create the desired conversionto electrical energy. The resulting signal is passed to the controlsignal processing circuitry 17 which performs the translation to afrequency band above the telephone communications band. The preferredembodiment of this circuitry is shown in FIG. 8 and described in detaillater on. The preferred embodiment calls for a transmission frequencycentered at 10.7 Mhz.

Signals generated by the control signal processing circuitry 17 arepassed to a coupling network 18. This network feeds the control signalsto the telephone network wiring 26 and allows video signals to pass fromthe wiring along the conductive path leading towards the televisionreceiver 22. The network also performs the functions of matching theimpedance of the video signal path to that of the telephone wiring,blocking low-frequency signals from the transceiver electronics,blocking the diversion of video energy towards the control signalprocessing circuitry 17, and blocking higher harmonics of the controlsignal, but not the fundamental of this signal from transmission to thetelephone wiring and from transmission along the conductive path leadingtowards the television 22.

The importance of these functions is described in the followingparagraphs. The detailed electronic design of the preferred embodimentof this network is shown in FIG. 7 and is described in detail later on.

Impedance matching ensures an efficient transfer of energy from thetelephone wiring to the electronics of the device. Just as in the caseof the video source transceiver, the efficient transfer of video energyacross this junction can be important in situations where the signalenergy is only marginally sufficient to produce a high quality picture.

Blocking telephone and other low-frequency communications signals fromtransmission to the electronics of the transceiver prevents anyinterference with those signals and also prevents disturbance of the DCpower supplied to telephone devices. The blocking should be such that itrenders the functioning of these communications totally transparent tothe connection and operation of the transceiver.

Blocking of video signal energy from transmission between the network 18and the control signal processing circuitry 17 is important because itprevents the reduction of video signal energy by diversion along thispath.

Blocking the harmonics, but not the fundamental, of the signal emergingfrom the control signal processing circuitry 17 is important becausesome of the harmonics may coincide with the frequencies used fortransmission of video. Because they will transmit to the television 22as well as to the telephone wiring, these harmonics can causeinterference if they are of sufficient strength. No information is lostin this process because the information in the harmonics of a signal iscompletely redundant with the information in the signal fundamental.

Unless the energy level of the control signal is very high, there is noneed to block the control signal from transmission across the network 18towards the television receiver 22. This is because television receiversignore energy outside the video channel to which they are tuned unlessthat energy is at a very high level. For example, televisions ignoreenergy at VHF channel 4 when they are tuned to VHF channel 5. Problemsalso do not occur when the RF converter 19 is required. In that event,the control signal is shifted in frequency along with the video signal,but it is rejected by the television tuner for the same reasons asbefore.

Because the control signal signal cannot cause interference or otherharm to the television transceiver, the isolation circuitry described bythe Robbins patent, which blocks this intelligence from the television,is unnecessary.

Signals passing along the path from the network towards the television22 encounter the RF converter 19. As mentioned earlier, if a low VHFchannel is used for transmission, frequency conversion at the televisionend is not necessary and signals can transmit directly from the couplingnetwork 18 to the television 22.

When channels below VHF 2 are used for transmission, the RF converter 19converts the video signal to a channel that is tunable by ordinarytelevisions. Because of potential interference problems, this channelshould be one that is not used by local broadcasting. (Interferencecould normally be avoided by connecting the transceiver via a shieldedcoaxial cable. Many older televisions, however, do not offer a shieldedinput port, and many modern televisions exhibit slight leakage fromother available ports such as twin lead ports.)

Because the video source transceiver outputs video signals at thetransmission frequency, and this transceiver 15, inputs signals at thatfrequency, the two units must obviously cooperate in their RF conversiondesigns. Three systems are disclosed herein for cooperation between theRF converters of the disclosed transceiver pair to transmit video at achannel below VHF 2. Under each of these systems, the signal is providedto the television 22 at one of two adjacent broadcast channels,according to a switch set by the user. In the U.S., this featureguarantees that the requirement of providing a signal at a channel notused for local broadcasting is fulfilled because, as described earlier,the U.S. FCC has ensured that one of two adjacent channels is alwaysunused in a given locality. A complete description of each of thesesystems is presented in the next section.

The television transceiver connects to the telephone wiring network 26via a cord terminated with a male RJ-11 plug. Just like the cord usedfor connection of the video source transceiver, this cord contains a lowpass filter 24, which creates an isolated port that allows connection oftelephone equipment 25 without loading down the video signal passingfrom the network to the transceiver.

Unlike the cord connecting the video source transceiver to the telephonewiring, it is not as critical to supply this transceiver with a cordwhose conductors are twisted. That is because the level of the videoenergy traversing the cord will be much lower, and will generate lessradiation.

Because the television to which this transceiver connects may haveanother source of video signals available, and because most televisionsonly have one port for input of signals at VHF frequencies, it may makesense to provide a switch that allows users to connect both sources andquickly choose between them. Because of the likelihood that no signalsfrom the two sources contain energy at the same channel, any device orcomponent that performs this function might also allow the addition ofthe two. Technology to achieve these signal combination options is wellknown.

Such a component, not shown in the drawings, could be an attachment thatconnected in series with the cable connecting to the television. Itmight be more convenient, however, to include this component as part ofthe transceiver. In that case, the transceiver would simply include acoaxial port for input of signals from a second source, and would beable to provide signals from either source, or the combination of thetwo, to the local television. Controls on the transceiver would allowthe user to choose the composition of the signal provided to thetelevision.

There is a possibility that, when receiving signals from a video sourcelocated relatively close by, this transceiver 15 may receive a signalwhose energy level is too high for the television to which it isconnected. In the event that the transceiver includes RF conversioncircuitry, the solution is to ensure that this circuitry can manage highsignal levels, and that a level within the range of most televisionreceivers is provided at the output. When a low VHF channel is used fortransmission and RF conversion circuitry is not required, one solutionis to provide attenuation circuitry, set automatically or manually, thatreduces the energy of the signal to a level within the dynamic range ofordinary televisions.

Systems for RF Conversion to Achieve Transmission below VHF Channel 2

As mentioned earlier, two RF conversion operations are required in orderto transmit the video signal across the wiring at a channel below VHF 2.At the video source end, the transceiver must convert the signal fromthe frequency at which it is supplied to a band between 6 Mhz and 54Mhz. The transceiver connected to the television must recover the signalfrom within this band and convert it to a channel tunable by ordinarytelevision receivers. Three systems for cooperation between theseconversion operations are described in the following paragraphs, alongwith their respective advantages and disadvantages.

Under each of the systems, the signal is provided to the television 22at one of two adjacent broadcast channels, according to a switch set bythe user. In the U.S., this feature guarantees that the requirement ofproviding a signal at a channel not used for local broadcasting isfulfilled because, as described earlier, the U.S. FCC has ensured thatone of two adjacent channels is always unused in a given locality.

The unusual nature of the conversion operations, combined with thenovelty of using these channels for a consumer video application, or forany video application other than the cable distribution functiondescribed earlier, make the resulting electronics a new consumerelectronic development.

The systems are summarized by the chart in FIG. 3. The preciseelectronic details of the various converters are not given becausetechnology to achieve these conversions is known, and would be withinthe ability of one of working skill in this field.

Under the first system, the video source transceiver derives its signalfrom a low VHF port and imparts a fixed downshift to produce one of twoadjacent channels. Signals spanning 24 Mhz to 30 Mhz or 30 Mhz to 36Mhz, for example, are produced from VHF channels 3 or 4 by a fixeddownshift of 36 Mhz. In the final step of this system, the RF converterin the television transceiver imparts an equivalent fixed upshift,restoring the signal to its original channel for delivery to thetelevision. The fixed downshifts mean that the choice of which of thetwo channels is actually used for transmission is determined by thesetting on the video source that chooses between VHF channel 3 or 4.

(There are a few video sources that supply signals at VHF channels 2 or3 instead of VHF channels 3 or 4. To account for these sources, theshifting should be designed to include bands covering at least 18 Mhz,rather than 12 Mhz.)

The advantage of this system is that the versatility already supplied bythe low VHF port of the video source is used to ensure that thetransmitted signal is supplied to the television at an unused channel.This enables the two RF converters to be designed to translate by afixed amount, reducing manufacturing costs.

The second system calls for the RF converter in the video sourcetransceiver to use the video signal from a baseband port to modulate acarrier to either one of two adjacent channels below VHF 2, according toa switch set by the user. (It would ordinarily make sense, of course,for the modulator to combine an audio signal, if available, togetherwith the video according to the NTSC or an equivalent format, and thento modulate using this combined signal.) In cooperation with thisconversion, the RF converter of the television transceiver againupconverts by a fixed amount. If the modulation created the channelsspanning either 24 Mhz to 30 Mhz or 30 Mhz to 36 Mhz, for example, anupshift of 36 Mhz would produce VHF channels 3 or 4, an upshift of 52Mhz would produce VHF channels 5 or 6, and an upshift of 150 Mhz wouldproduce VHF channels 7 or 8.

The primary advantages of this design over the first are thoseadvantages, described earlier, that accrue to designs that derivesignals from the baseband port of the video source. There is also aconvenience in that inexpensive modulation ICs are available thatprovide much of the circuitry necessary to build video modulators withoptions for one of two carriers in the 10 Mhz to 100 Mhz range. Finally,being able to choose adjacent VHF channel pairs other than VHF channels3 or 4 allows combination of the signal passed to the television withsignals from most common video sources.

Two variations to the second system are now disclosed. In the firstvariation, the switch will be automatically controlled. It will rely oncircuitry that samples the telephone line to detect the presence ofbroadcast energy at either of the two channels used to provide thesignal to the television. (Broadcast energy will be on the telephoneline because it acts as an antenna to some extent.) It will set the RFconverter in the video source transceiver to provide a transmissionfrequency so as to ensure that the channel ultimately presented to thetelevision receiver will be one unused for local broadcast.

In the second variation, the RF converter in the video sourcetransceiver will simultaneously provide the video signal at both of thetwo adjacent channels below VHF 2, so that when the televisiontransceiver converts the 12 Mhz band spanning these channels, itproduces signals at both of the two adjacent tunable channels.

The third system also calls for the video source transceiver to deriveits signal from the baseband port, but it includes an RF converter thathas only a single carrier which modulates the signal to a single fixedchannel that is used for transmission. The RF converter in thetelevision transceiver then performs either one of two upwardconversions, according to a switch set by the user, resulting in one oftwo adjacent low VHF channels. If the transmission channel spanned 24Mhz to 30 Mhz, for example, upshifts of 36 Mhz and 42 Mhz would produceVHF channels 3 and 4, and upshifts of 52 Mhz and 58 Mhz would produceVHF channels 5 and 6.

In a variation of this strategy the RF conversion component of thetelevision transceiver allows continuously variable manual tuning, inplace of two fixed upshift conversions. This tuning must, of course,allow the signal presented to the television to span two consecutivechannels. The provision of manual tuning reduces the precision requiredfor both converters, resulting in a certain economy.

Like the second design, the two variations of the third design alsoenjoy the advantages of baseband input, and the advantage of being ableto output adjacent VHF frequencies other than VHF 3 and 4. The mainadvantage over the second design is that the single optimal sub-VHF 2channel, in terms of radiation, attenuation, interference from broadcastsources, legal restrictions, and expense of conversion electronics, canbe chosen.

Because of these advantages, and because transmission over channelsbelow VHF 2 affords reliability which is of enormous importance inconsumer products, this third system is the preferred embodiment.Furthermore, the fixed and not the variable tuning is preferred becauseof the importance of convenience in consumer products. The preferredchannel spans from 24 to 30 Mhz because there is a liberalization ofU.S. FCC radiation restrictions below 30 Mhz, and because the conversionelectronics are slightly more expensive when lower frequencies are used.Finally, it is preferred to present the signal to the television ateither VHF 5 or 6, because of the advantages of combining those channelswith broadcast signals or other video sources. (These preferences maychange as a result of data not currently available to the inventors suchas, specifically but not exclusively, information regarding thefrequency, strength, and location of RF sources throughout the U.S. thatmay provide interference at channels below VHF 2.)

Two further variations to the third system are now disclosed. In thefirst of these, the switch will be automatically controlled. It willrely on circuitry to detect the presence of broadcast energy, to set theRF converter of television transceiver to convert the transmitted videoenergy to the channel unused for local broadcast. In the secondvariation, the RF converter of the television transceiver willsimultaneously provide the video signal at both of the two adjacenttunable channels.

Description of the Special Television Receiver

The transceiver pair disclosed above provides an ability to view andcontrol a video source at a remotely located television. A significanteconomy can be achieved, however, if the function of the disclosedtelevision transceiver is internalized in the television electronics.

A special television 30, shown in Figure, provides such a combination.This television is intended to cooperate with the video sourcetransceiver described above. It comes equipped with a cord that includesa low-pass filter 32, similar to those used with the transceiversdescribed earlier, for allowing telephone equipment 33 to share the samejack without loading down video signals on the wiring.

The television includes an IR sensitive diode 42, for convertinginfrared signals into electrical signals. These signals are passed tothe special control signal processing circuitry 37 and the standardcontrol signal processing circuitry 41. The standard circuitry 41 reactsto these signals to execute control over television operations in theordinary manner. The special control signal processing circuitry 37translates the electrical version of the control signals to a frequencyband above the highest frequency used for ordinary telephonecommunications, and passes them to the coupling network 34.

The functions performed by the special control signal processingcircuitry 37 are the same functions performed by the control signalprocessing component included in the transceiver, described earlier,that connects to the television. The preferred embodiment of thecircuitry is also the same. This embodiment is shown in FIG. 8 and isdescribed later on.

The coupling network 34 allows the control signals to pass to thetelephone network wiring 31 and video signals to transmit from thewiring along the conductive path leading towards the RE converter 35.The network 34 also performs the important functions of matching theimpedance of the conductive path leading to the RF converter to theimpedance of the telephone wiring, blocking low-frequency signals fromthe television electronics, blocking the flow of video signals towardsthe special control signal processing circuitry 37, and blockingharmonics of the control signal, but not the fundamental of this signalfrom the telephone line and the conductive path leading towards the RFconverter 35.

The functions performed by this network are the same functions performedby the coupling network included in the television transceiver describedearlier. An explanation of the importance of these functions wasincluded in the description of that device. The preferred embodiment ofthe network used here is also the same. This embodiment is shown in FIG.7 and described later on.

Both the video and RF control signals pass from the coupling network 34to the RF converter 35. That component will convert the video signal toa channel that is tunable by ordinary television tuning electronics. Ifa low VHF channel is used for transmission across the wiring, however,ordinary television tuners can tune to the transmitted signal and thiscomponent is not necessary.

Signals emerging from the RF converter 35 transmit to the RF signalcombiner 36. (If the RF converter 35 is not needed, signals flowdirectly from the coupling network 34 to this combiner.) The RF combiner36 will accept video signals from a local video source 43 if one isavailable. It will add signals from the two sources, or will choose thesignals from one source or the other to pass along to the tuning section38. The final composition of the signals passed to the tuning section 38will be set by manual controls on the television 30 or by infraredcontrol signals received by the IR sensitive diode 42.

The RF converter 35 disclosed herein can cooperate with the RF converterof the video source transceiver using one of the three alternativesystems, described earlier, for cooperation between RF conversioncomponents at the two ends of the communication path. The RF converter35 included in the television will simply perform the same functions asthe RF converter of the television transceiver described earlier, whilethe RF converter in the video signal transceiver will perform thecorresponding conversion.

A variation of the third system for cooperation between converters isnow disclosed for the case of the special television receiver 30. Underthis variation, the RF converter 35 demodulates the video signal itreceives, and injects that signal into the television at the point whereit ordinarily expects demodulated signals. (The demodulated signal willnot go into the combiner in this case, eliminating the need for thatcomponent. Signals from a local video source 43 will pass to the tunerwithout combination.) This variation liberates the converter fromproviding a signal at either one of two adjacent channels, and might beless expensive, overall, than the alternative.

Note that the RF converter 35 is not necessary if the television tuner38 can tune to signals below VHF channel 2. This converter is offered asan alternative to providing the television with a special tuner becauseit may be less expensive to adapt the design of an ordinary televisionby adding this simple component.

In the preferred embodiment, the video signal transmits across thewiring at a frequency below VHF channel 2, and the RF converter isrequired because the television tuning section 38 tunes in only theordinarily tunable channels. A channel below VHF 2 is preferred becauseof the decreased probability of picture degradation, and the RFconverter is preferred because the inventors believe that it is lessexpensive to adapt the design of an ordinary television by adding aconverter.

A transmission channel spanning 24 Mhz to 30 Mhz is preferred, and it ispreferred that the RF converter of the television convert that channelupwards by either 52 Mhz or 58 Mhz to VHF channels 5 or 6, according toa switch setting on the television, or a command from the infraredcontroller. This embodiment follows the preferred system, presentedearlier, for coordination between the RF converter of the video sourcetransceiver and the RF converter of the television transceiver. Thejustifications used earlier also apply to this case. The option ofdemodulating the video signal is not currently preferred because theexpense of this option is not clear.

Television 30 is novel in the following three respects. First, itconnects to active telephone networks, without causing interference, toderive video signals, in addition to the video signals it derives fromother sources. Secondly, in addition to detecting infrared signals forthe purposes of controlling television functions, it converts thesesignals to electrical RF energy, and passes them on to the telephoneline for controlling the video source in cooperation with anotherdevice. Finally, it is able to tune to signals at channels below VHF 2.

When the television 30 cooperates with the video source transceiver 1described above, they allow the user to watch and control a video sourcefrom a remote location. To further increase the usefulness of thiscombination without significant extra cost, a unique combination of thispair of devices with a special piece of known technology is disclosed inthe following two paragraphs.

To control the video source from the area wherein the special televisionreceiver 30 is located, the infrared transmitter unit that controls thatsource must ordinarily be available at that location. This is not alwaysconvenient, because this unit is obviously often required at thelocation of the video source. If the television 30 is provided with itsown infrared controller, inclusion of the command set of the videosource controller as a subset of the available commands significantlyincreases the convenience of the system without significant extra cost.

Recently, infrared control units with large command sets that includethose of many different controllers have become available, as have otherunits that have the ability to learn the command sets from virtually anyother controller. The novel combination disclosed here adds a similaruniversal controller together with the disclosed cooperating television30 and transceiver 1. This will significantly increase the usefulness ofthat pair of devices.

Systems for Avoiding Interference from Broadcast Sources

The signals transmitted by the devices disclosed above travel fromsource to receive via conduction across telephone wiring. A potentialproblem of this technique, described earlier, is that RF broadcastenergy from nearby sources can be received by the wiring and interferewith the signal of interest. Under the design option where the videosignals transmit at a low VHF channel, the devices provide signals at achannel unused by any local service. This protection is not availablewhen the video signals transmit at frequencies below VHF channel 2. Thefollowing factors, however, make the possibility of interferenceunlikely:

a) The signal-to-noise ratio required for a quality video picture,approximately 40 dB, is relatively low. Interfering signals must haveenergy levels within 40 dB of the signal of interest to visibly degradea picture.

b) The signal of interest is conducted directly on to the wiring. Theinterfering signal must be received by the wiring acting as an antenna,a much less efficient method of creating conductive energy.

c) The ability of the wiring to receive broadcast energy decreases withdecreasing frequency.

d) The level of the signal of interest can be boosted to reduce thepotential of interference. (Because of legal and technologicalconstraints, however, there are limits to the level to which this energycan be boosted.)

Despite these factors, tests have indicated that interference can occur.Three methods for avoiding interference problems are discussed below.

a) One can choose a frequency band that is less likely to be used bymany transmitters operating at high power near residential areas. Thisstrategy requires a survey of frequency allocations and broadcastingpatterns. Preliminary investigation by the inventors revealed thatamateur radio is allocated narrow bands at 7 Mhz, 14 Mhz, 21 Mhz, and 28Mhz, conveniently leaving gaps of 7 Mhz—just right for video.

b) The video source transceiver can simultaneously transmit its signalover two frequency bands, and the signal that encounters lessinterference can be chosen, at the television end, to provide thepicture.

In the case of the cooperating transceiver pair, the video sourcetransceiver simultaneously transmits the same signal over two differentand non-overlapping channels below VHF channel 2. The RF converter ofthe transceiver that connects to the television chooses, according to amanual control or an automatic process, to accept one of the twochannels, converting the energy within that channel to a tunablefrequency unused for local broadcast. (Circuitry to automatically choosethe less “noisy” channel would have to include means to detect thepresence of broadcast energy within each of the two channels.)

In the case of the special television that cooperates with the videosource transceiver and includes a special RF converter, that converterperforms the same functions as the converter in the televisiontransceiver. Under the design option wherein the television tuner cantune directly to signals below VHF channel 2 (and a converter is notinvolved) the tuner simply tunes to one channel or another.

c) Because the information at the edges of an NTSC video signal isredundant, these edges can be filtered out before presentation to atelevision, removing any interfering energy at those edges.Specifically, the first 1.25 Mhz in an ordinary NTSC channel, known asthe vestigial side band, can be filtered out before presentation to thetelevision. This will reduce the video bandwidth from 5.75 Mhz to 4.5Mhz, reducing opportunities for interference. In the event that researchshows that this causes some degradation of picture quality, thevestigial side band can be recreated free from interference within theshielded television transceiver, using known techniques.

The upper 0.25 Mhz of the full 5.75 Mhz video signal can also befiltered without significant reduction in picture quality. Trimming thisenergy, however, will remove the audio information, which is locatedimmediately above the video information. The solution is to transmit theaudio signal at a different frequency, converting that signal to itsproper place before presentation to the television.

Systems for Simultaneous Transmission of a Second Video Signal

A video source transceiver connecting a second source to the sameresidential wiring network obviously has to transmit its signal at adifferent frequency in order to operate simultaneously with the firstsource. Ideally, this transceiver cooperates with the televisiontransceiver unit without requiring any design changes to thattransceiver. That allows the most economical design for the primarytransceiver pair, and still allows expansion of the system to include asecond source.

If low VHF channels are used for transmission, design of the secondvideo source transceiver is straightforward. That transceiver simplytransmits its signal at one of a second pair of adjacent low VHFchannels. If, for example, the primary video source transceiver uses VHFchannel 5 or 6, the secondary transceiver could use VHF channel 2 or 3.The television transceiver described earlier will supply both signals tothe television receiver without any design changes.

If the primary transmitter uses a channel below VHF 2, and the secondarytransceiver uses a low VHF channel, a slight alteration in the design ofthe transceiver that connects to the television is required. Thealteration calls for an extra signal path to the television thatbypasses the RF converter. That path includes the unshifted low VHFsignals which could be easily combined with the signal that wasconverted up by the RF converter. The channel generated by the RFconverter, of course, will have to be different from the channel usedfor transmission of the second source.

Things are more complicated when both video signals transmit at channelsbelow VHF 2 because the television transceiver must convert a secondsignal to a second tunable channel that is not used for localbroadcasting. The shift in frequency required by the second signal,moreover, may not necessarily be the same as that required by the firstsignal. The largest problem, however, may be finding an extra 6 Mhz thatis free from broadcast source interference.

Extra transceivers that transmit video over the same channel as theprimary transceiver can be connected, of course, as long as a viewer candisable all but one of the resulting group of connected transceivers. Inthe following paragraphs, two designs are disclosed for systems thatallows a user to quickly, conveniently, and remotely activate exactlyone of several connected video source transceivers transmitting at thesame frequency.

The first design calls for the signal from all but one of thetransceivers to be blocked from transmission on to the wiring. Theblocking is accomplished by the touch tone switch 8 shown in FIG. 1.This switch connects on the cord between the transceiver and thetelephone jack, and contains a low pass filter, or other means thatcompletely block signals above a frequency that is below the frequenciesused for video transmission. It has two settings, one of which enablesthe filter and the other which defeats it. The switch reacts to the DTMF(dual tone multi frequency) touch tones commonly created by telephones,allowing users to conveniently select the active source from among theseveral connected. Any logical command system will suffice. Theelectronic details of this switch are not shown because RF filters andtouch tone controls are well known.

The second design calls for each of the video source transceivers thattransmit at the same frequency to derive its AC power via powerlineswitches similar to those built by the X-10 Corporation. These switchesconnect between power cords and AC outlets. They detect high frequencycontrol signals fed onto the wiring by a remote device, and respond byblocking or enabling power to pass along the power cord to the connectedelectrical device. This allows one to remotely control the AC power toany device in a residence via control signals sent through the ACwiring. Thus, a user could conveniently select one of many sourcessharing a transmission frequency by activiating the AC power for thetransceiver of that source and none of the others.

Because the first design uses ordinary touch tone telephones to the sendsignals that establish the identity of the active transceiver, it ispreferred over the second design, which requires special transmitters tosend those signals.

Description of the Adaptor for Central Telephone Switching Devices

As mentioned in the introduction, a reliable conductive path is notalways available in residences where each jack is wired directly to acentral electronic interface unit that connects to the public telephonesystem. Because of the topology of these networks, potential conductivepaths from one jack to another will always traverse this unit, wheretheir continuity is likely to be broken.

To allow the disclosed devices to operate on such a network, aninexpensive adaptor 52 is disclosed. This adaptor is shown in FIG. 5.

Normally, the wiring leading from the jack 50 in the first area 51 wouldconnect to the port 56 on the electronic switching unit 58 dedicated tothe first area. Similarly, the wiring leading from the jack 53 in thesecond area 54 would connect to the port 57 on the unit dedicated to thesecond area.

The adaptor 58 reroutes these connections through a pair of low passfilters 59 and 60. These block the transmission of high frequencysignals away from the switching unit, eliminating attenuation. Thefiltering can be achieved by the same pair of inductors disclosedearlier that achieve low pass filtering of any telephone equipment thatshares a jack with either of the two cooperating transceivers.

The high pass filter 61 connects the paths leading from the first area51 to the second area 54 at high frequencies, completing the conductivepath for video and control signals between the associated jacks.Transmission of low-frequency energy across this path is blocked,maintaining separation of the telephone and other low-frequencycommunication between each jack and the switching unit. In the preferredembodiment, the high pass filtering is achieved by a pair of 100 pFcapacitors, connected as shown.

The problem of inadequate video signal energy in the area where thetelevision is located was described earlier. Because the disclosedadaptor offers access to the signal near the midpoint of itstransmission path, it offers a new solution to this problem. Thesolution, not shown in the drawings, calls for an amplifier to accompanythe adaptor. A path leading from a video source could be passed throughthis amplifier just before connection to the adaptor. In this way, partof the total amplification required could be imparted at the videosource transceiver, and the other part at the switching unit. This wouldreduce the peak signal power at any point for a given level of totalamplification, thus reducing the maximum level of radiation.

For systems that also transmit control signals, a bypass around theamplifier for transmission of these signals would have to be made. Thebypass would simply be a conductive path around the amplifier includinga filter to block video signals. Similarly, the input to the amplifierwould require a filter to block out control signals.

Because the technology disclosed herein is not limited to residentialnetworks, and because “star” wiring configurations including a centralswitching unit are very common among telephone networks installed incommercial buildings, including but not limited to offices and hotels,the disclosed adaptor has the important function of enabling thoseinstallations to benefit from this video transmission technique.

Details of the Coupling Network Circuitry

The earlier descriptions of the cooperating transceivers referred tocoupling network circuitry in functional terms. The preferred embodimentof this circuitry is now presented in detail.

FIG. 6 shows the preferred embodiment of the coupling network of thevideo source transceiver. The principal element of this network is atransformer wound on a toroid core 71. There are three isolated windingscorresponding to the ports leading to the telephone network wiring 72,the video signal amplifier 73, and the control signal processingcircuitry 74. The special winding method shown for the phone line portserves to maximize its balance.

The low pass filter 75 on the port leading to the control signalprocessing circuitry 74 blocks signals above the frequency used forcontrol signals. This blocks the video energy, preventing that energyfrom disturbing the processing of the control signals, and preventsloading of video signals on the telephone line.

There are different numbers of windings on the toroid core for the threedifferent ports. (The number of windings shown are only for purposes ofillustration.) The turns ratios determine the impedance matching betweenthe telephone port and the other two ports. Different ratios are neededbecause the video port and the control signal port have differentimpedances at different frequencies.

The impedance matching for video signals is governed strictly by theturns ratio between the telephone port and the video port. It isindependent of the windings on the IR port because the filter 75prevents video energy from flowing towards that port.

The capacitor 77 serves as a high pass filter to block and present ahigh impedance to DC and low-frequency energy, preventing anydisturbance of ordinary telephone communications at those frequencies.

FIG. 7 shows the preferred embodiment of the coupling network of thetelevision transceiver. The principal element of this network is again atransformer wound on a toroid core 80. There are three isolated windingscorresponding to the ports leading to the telephone line 81, thetelevision receiver 82, and the control signal processing circuitry 83.The special winding method for the telephone line shown earlier is notnecessary because maximum balance is not as important due to the lowerenergy level of the video signals at this end.

The low pass filter 84 on the control signal port passes the 10.7 Mhzsignal but blocks harmonics of 10.7 Mhz. These harmonics, whoseintelligence is redundant with the intelligence in the fundamental,could potentially interfere with the video signals. The resultingcontrol signal passes on to both the telephone line and to thetelevision. To prevent loading down the video signal, the filter 84 alsoblocks video signals from the control signal port.

There are different numbers of windings on the toroid core 80 for thethree ports. (The number of windings shown are only for purposes ofillustration.) The turns ratios determine impedance matching. Becausethe level of the control signal is high enough to easily survive theinfluence of any impedance mismatch, the impedance of the ports needonly be properly matched at video frequencies, and only between thetelephone line port and the video port.

The capacitor 85 serves as a high pass filter to block DC andlow-frequency energy and prevent any disturbance with ordinary telephonecommunications at those frequencies.

It should be understood that various changes and modifications to thepreferred embodiment of the coupling network described above will beapparent to those skilled in the art. For example, other windingconfigurations are possible, including but not limited to broadbandmultifilar configurations. These and other changes can be made withoutdeparting from the spirit and scope of the invention.

Details of the Control Signal Processing Circuitry

The earlier descriptions of the cooperating transceivers referred tocontrol signal processing circuitry in functional terms. The preferredembodiment of this circuitry is now presented in detail.

FIG. 8 shows the details of the control signal processing circuitry inthe television transceiver that detects infrared signals, and translatesthem to RF energy. This circuitry consists of a photodiode 101, ahigh-gain amplifier stage 102, a thresholded zero crossing detector 103,and a gated oscillator 104. These elements are arranged to produce amodulated RF carrier whose envelope is a replica of the infrared signalwaveform.

The RF carrier is coupled to the telephone line through the couplingnetwork 105. The coupling network shown in FIG. 8 is designed only tofeed control signals on to the network. The coupling network of thepreferred embodiment, which is designed to include recovery of videosignals from the wiring, is shown in FIG. 7 and was described earlier.

Photodiode 101 functions as a current source with current proportionalto the intensity of incident light within its spectral passband. Thisphotocurrent is converted to a voltage by resistor 110 and amplified byintegrated circuit 111. Capacitors 112 and 113 reduce the low frequencygain of the amplifier stage to render the receiver insensitive toambient light sources, such as sunlight or AC powered interior lightingwith a nominal 120 Hz flicker rate. Transistor 114 buffers andlevel-shifts the output of the amplifier, and passes the signal to thezero crossing detector section 103.

The output of the detector section 103 is a bi-level waveform thatcorresponds to the received infrared signal. This output is high whenthe input signal exceeds its long term average, and low otherwise. Noiseeffects are suppressed by disabling the bi-level signal except when theexcursions of the input signal exceed a fixed threshold. The bi-levelwaveform is fed to the oscillation section to enable or disable the RFcarrier, thus generating the desired AM signal at an RF frequency.

The output of comparator 122 is set high when the optical flux isgreater than the long term average, which is formed using an averagingtime of 100 msec, as determined by capacitor 127.

The noise condition is detected by comparator 123. It sets its outputlow when the input signal is a fixed amount greater than the long termaverage. This threshold is set so that noise will not cause it to beexceeded. The threshold may be changed as desired by altering the ratioof resistors 116 and 117 to provide different levels of noisesuppression.

Capacitor 126 causes a low output from comparator 123 to remain low fora fixed period. Comparator 124 inverts this output, and comparator 125is used to merge that output with the the output from comparator 122. Inthis manner, the output exits to the oscillator section withoutinterruption when a genuine signal is present, and dies off quickly whenthe signal disappears.

In the oscillator section, transistor 118 is wired as a Colpittsoscillator with frequency determined primarily by capacitor 119 andvariable inductor 120. In the preferred embodiment, this frequency isselected to be 10.7 Mhz because of the good availability of tuningcomponents at this frequency. When the oscillator is disabled bycomparator 125, an idle current of several milliamps is drawn throughthe inductor and resistor 121. This idle current provides rapid turn-onof the oscillator within a microsecond when the oscillator is activatedby comparator 125 going to a high impedance state at its open-collectoroutput.

FIG. 9 shows the control signal processing circuitry in the video sourcetransceiver that uses control signals recovered from the network torecreate the infrared pattern detected by the television transceiver.The circuitry consists of an RF amplifier/detector 131, threshold/drivercircuitry 132, and an output LED 142.

The control signals are recovered from the telephone line by thetelephone coupling network 130. The coupling network shown in FIG. 9 isdesigned only to recover control signals from the network. The couplingnetwork of the preferred embodiment, which is designed to includetransmission of video signals onto the network, is shown in FIG. 6 andwas described earlier.

Signals recovered from the network pass through RF filter 133. Thisfilter, which is part of the coupling network, is a ceramic filter withbandpass centered at 10.7 Mhz and a bandwidth of 280 khz. This matchesthe characteristics of the RF signals generated by the infrared signalprocessing circuitry described above.

The RF amplifier/detector 131 amplifies and envelope detects the signalsthat pass through the filter. In the preferred embodiment, this functionis performed by an integrated circuit 134 of type 3089, which iscommonly used as an IF amplifier in commercial FM radios. The detectedoutput is logarithmically related to the amplitude of the RF inputsignal.

The detected output is buffered by Darlington transistor 140. Comparator141 provides threshold detection by comparing the instantaneous envelopeof the detected signal to the peak envelope of the detected signal. Thecomparator turns on LED 142 whenever the envelope exceeds a fixedpercentage of the peak. Resistors 143 and 144 set the threshold of thetransmitter; the LED will not be driven on unless a minimum signal levelat the input of the integrated circuit 134 is exceeded.

While the foregoing has been provided with reference to one or morepreferred embodiments, various changes within the spirit of theinvention will be apparent to those of working skill in this technicalfield. Thus, the invention should be considered as limited only by thescope of the appended claims.

1. A method for communicating information over a conductive path,comprising: encoding a first information set in a first signal, whereinthe power spectrum of the first signal is substantially confined withina plurality of bands, the bands in the plurality of bands arenon-overlapping frequency bands, and a first band extends between alowest frequency in said plurality of bands and a highest frequency insaid plurality of bands, where the first band is not one of theplurality of bands, at least some information in the first informationset is encoded in each band of the plurality of bands, where theinformation encoded in any two bands of the plurality of bands is eitherthe same or different, at least part of the first information set issubstantially recoverable from the portion of the first signal thatoccupies any one band in the plurality of bands, and the firstinformation set is substantially recoverable from any portion of thefirst signal created by excluding the part of the first signal thatoccupies any one of the bands in the plurality of bands; encoding asecond information set in a second signal, where the first signal andthe second signal are electrical signals; and transmitting the firstsignal onto the conductive path at a first point and transmitting thesecond signal onto the conductive path at a second point, wherein thefirst point and the second point are at different locations on theconductive path, the first signal is transmitted during a first set oftime intervals, where the first set of time intervals is non-empty, thesecond signal is transmitted during a second set of time intervals,wherein the second set of time intervals is non-empty, and the first setof time intervals and the second set of time intervals are substantiallynon-overlapping.
 2. A method according to claim 1, wherein the powerspectrum of the second signal is substantially confined within the firstband.
 3. A method according to claim 1, wherein a lowest frequency inthe first band is above 3 Khz.
 4. A method according to claim 1, whereineither the first signal or the second signal is transmitted onto theconductive path while signals with power spectrum below 3 KHz areblocked by presenting a high impedance to signals with power spectrumbelow 3 KHz on said conductive path.
 5. A method according to claim 2,further comprising transmitting a baseband signal onto the conductivepath while transmitting the first signal, the power spectrum of thebaseband signal being substantially confined between 20 Hz and 3 KHz. 6.A method according to claim 5, wherein the amplitude of the basebandsignal is at least 30 volts RMS.
 7. A method according to claim 2,further comprising powering an electronic device using current flowingon the conductive path.
 8. A method according to claim 2, wherein a setof one or more mutually non-overlapping non-zero width gap bands arewithin the first band, wherein each gap band in the set of gap bands isnon-overlapping with the bands in the plurality of bands.
 9. A methodaccording to claim 1, wherein the bands in the plurality of bands have asame width.
 10. A method according to claim 9, wherein each of the oneor more gap bands substantially overlaps a different radio bandallocated to amateur radio transmission.
 11. A method according to claim10, wherein a first gap band of said set of gap bands substantiallyoverlaps a corresponding radio band and includes at least one of thefrequencies: 7 MHz, 14 MHz, 21 MHz, or 28 MHz.
 12. A method according toclaim 2, further comprising receiving the first electrical signal fromthe conductive path and recovering substantially all of the firstinformation set from the first electrical signal.
 13. A method accordingto claim 1, wherein the power spectrum of the second signal issubstantially confined to frequencies above and below the firstfrequency band.
 14. A method according to claim 13, further comprisingreceiving the first electrical signal on the conductive path andrecovering substantially all of the first information set from thereceived first electrical signal.
 15. A method according to claim 2,further comprising receiving the first electrical signal at a thirdpoint on the conductive path and recovering substantially all of thefirst information set from the received first electrical signal, whereinthe first, second, and third points are at different locations on theconductive path.
 16. A method according to claim 15, further comprisingtransmitting telephone signals onto the conductive path at voicebandfrequencies while simultaneously transmitting at least part of saidfirst signal onto the conductive path.
 17. A method according to claim13, further comprising powering an electronic device using currentflowing on the conductive path.
 18. A method according to claim 13,wherein a set of one or more mutually non-overlapping non-zero width gapbands are also within the first band, wherein each gap band in the setof gap bands is non-overlapping with the bands in the plurality ofbands.
 19. A method according to claim 15, wherein the bands in theplurality of bands have a same width.
 20. A method according to claim19, wherein each of the gap bands substantially overlaps a correspondingradio band allocated to amateur radio transmission.
 21. A methodaccording to claim 20, wherein a first gap band of said set of gap bandssubstantially overlaps a radio band and the first gap band includes atleast one of the frequencies: 7 MHz, 14 MHz, 21 MHz, or 28 MHz.
 22. Amethod according to claim 1, further comprising allowing the firstsignal and the second signal on the conductive path to pass whileblocking signals within voiceband.
 23. A method according to claim 22,wherein the blocking of voiceband signals includes presenting a highimpedance to voiceband signals to substantially prevent attenuation ofvoiceband signals.
 24. A method according to claim 1, further comprisingallowing signals within voiceband on the conductive path to pass andblocking signals above voiceband, wherein the signals within voicebandare telephone signals.
 25. A method according to claim 24, wherein theblocking of signals above voiceband includes presenting a high impedanceto signals above voiceband to substantially prevent attenuation ofsignals above voiceband.
 26. A method according to claim 1, wherein onthe conductive path there are reflections of the first signal that arecreated by impedance discontinuities, and wherein substantially all ofthe first information set is recoverable despite the reflections.
 27. Amethod according to claim 1, wherein the first information set includesvideo information.
 28. A method according to claim 27, furthercomprising converting the video information in the first information setto moving images.
 29. A method according to claim 1, wherein the firstinformation set includes audio information.
 30. A method according toclaim 29, further comprising converting the audio information to sound.31. A method for communicating information over a conductive path,comprising: encoding a first information set in a first signal andencoding a second information set in a second signal, wherein the firstsignal and the second signal are electrical signals that have powerspectrums that are substantially confined within a first frequency band,and wherein a lowest frequency of the first frequency band is above 3KHz; transmitting the first signal onto the conductive path at a firstpoint, and transmitting the second signal onto the conductive path at asecond point, wherein the first signal is transmitted during a first setof time intervals, the second signal is transmitted during a second setof time intervals, and the first set and the second set of timeintervals are substantially non-overlapping; and receiving the firstsignal at a third point on the path and recovering substantially all ofthe first information set from the first signal received at the thirdpoint, wherein the first, second, and third points are at differentlocations on the conductive path.
 32. A method according to claim 31,further including powering an electronic device using current flowing onthe conductive path.
 33. A method according to claim 31, furtherincluding transmitting a baseband signal onto the conductive path duringat least some of the first set of time intervals, the power spectrum ofthe baseband signal being substantially confined between 20 Hz and 3KHz.
 34. A method according to claim 33, wherein the amplitude of thebaseband signal is at least 30 volts RMS.
 35. A method according toclaim 31, further comprising transmitting telephone signals onto theconductive path at voiceband frequencies while simultaneouslytransmitting at least part of said first signal onto the conductivepath.
 36. A method according to claim 31, further comprising allowingsignals within voiceband on the conductive path to pass and blockingsignals above voiceband, wherein the signals within voiceband aretelephone signals.
 37. A method according to claim 36, wherein theblocking of signals above voiceband includes presenting a high impedanceto signals above voiceband to substantially prevent attenuation ofsignals above voiceband.
 38. A method according to claim 31, furthercomprising providing a gap band, wherein a lowest frequency of the gapband is above a lowest frequency of the first frequency band and ahighest frequency of the gap band is below a highest frequency of thefirst frequency band, and substantially all of the power spectrum of thefirst signal occupies the part of the first frequency band that excludesthe gap band.
 39. A method according to claim 38, wherein the gap bandsubstantially overlaps a radio band allocated to amateur radiotransmission.
 40. A method according to claim 39, wherein the radio bandincludes at least one of the frequencies: 7 MHz, 14 MHz, 21 MHz, or 28MHz.
 41. A method according to claim 31, further comprising allowingsignals above voiceband on the conductive path to pass and blockingsignals within voiceband, wherein the signals within voiceband aretelephone signals.
 42. A method according to claim 41, wherein theblocking of voiceband signals includes presenting a high impedance tovoiceband signals to substantially prevent attenuation of voicebandsignals.
 43. A method according to claim 31, further comprising allowingsignals within voiceband on the conductive path to pass and blockingsignals above voiceband, wherein the signals within voiceband aretelephone signals.
 44. A method according to claim 43, wherein theblocking of signals above voiceband includes presenting a high impedanceto signals above voiceband to substantially prevent attenuation ofsignals above voiceband.
 45. A method according to claim 31, wherein onthe conductive path there are reflections of the first signal that arecreated by impedance discontinuities, and wherein substantially all ofthe first information set is recoverable despite the reflections.
 46. Amethod according to claim 31, wherein the first information set includesvideo information.
 47. A method according to claim 46, furthercomprising converting the video information in the first information setto moving images.
 48. A method according to claim 31, wherein the firstinformation set includes audio information.
 49. A method according toclaim 48, further comprising converting the audio information to sound.